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With the progress of two teams generating human embryonic stem cells from adult patients by means of cloning, scientists are one step closer to another means of delivering patient-specific treatments in the clinic.

In mid April, Cell Stem Cell published a paper by Young Gie Chung et al on their success generating stem cell lines from a 35-year-old and a 75-year old.

Two weeks later, the paper by Dieter Egli and his team at the New York Stem Cell Foundation appeared in Nature detailing their success generating the first patient specific line of stem cells from a woman with Type 1 diabetes.

In both cases, refining the protocols developed last year by Shoukhrat Mitalipov for somatic cell nuclear transfer, the researchers used healthy oocytes from donors, removed the eggs' nuclei and substituted a nucleus from the somatic cell of the adult patients. The cells were then 'jump started' by electric pulse into developing like a normal embryo.

At the blastocyst stage, the scientists were able to derive stable embryonic stem cell lines; they were further able to differentiate these into various cell types, demonstrating viability for therapeutic use.

In Egli's case, the goal was generating cells that produce and secrete insulin showing that this technique should be useful for the development of cell replacement therapies for Type 1 diabetes.

When the cells were injected into mice, he said, "they mature into glucose responsive beta cells and secrete insulin into the bloodstream."

For Susan Solomon, CEO of the NYSCF, it means researchers now have another reliable tool with which to provide future therapies for people who suffer from diabetes, and, potentially, other diseases. In the official release, she said:

This advancement toward potential regenerative cell replacement therapies is significant not only for diabetes but also for many other diseases and conditions, including Parkinson's, macular degeneration, multiple sclerosis, and damaged bones, among others. While there remain additional research hurdles to overcome before this work can reach the clinic, we are thrilled that our scientists have once again taken the lead in breaking down barriers that face the entire field.

Generating robust stem cells via SCNT, also called therapeutic cloning, was not considered a practical option before the breakthroughs by Mitalipov, Egli et al. The approach was further tainted by the scandal surrounding Korean scientist Hwang Woo-Suk's claims of success in cloning cell lines in 2005. A majority of scientists and the public also believe that reproductive cloning should be banned. (The U.S. still has no law that outlaws reproductive cloning.)

Although, early on (prior to 2006), the SCNT approach had been considered one of the hottest areas of research, according to Egli, it was eclipsed when Shinya Yamanaka developed the means to directly reprogram adult somatic cells into induced pluripotent stem cells (iPSCs) without the use of any embryos.

After Yamanaka's breakthrough, for which he won the Nobel Prize in 2012 for Medicine, the majority of stem cell researchers focused on this approach and the SCNT approach was largely passed over.

Most stem-cell biologists shifted focus as convenient technologies for making iPS cells became established, but Egli did not. “I didn't think it was right to only try one approach when it was so important to find cures for these diseases,” he says.

He thinks that iPS cell lines work well for drug screening and basic research questions, but it is still unclear whether iPS cells or ES cells will work best as therapies. “If you had a choice, you would pick the one from nuclear transfer rather than iPS,” he says. This is because iPS cells often do not become completely reprogrammed or may become warped during the reprogramming process, which could make them less stable.

If the SCNT approach does promise more robust cell lines, the question arises, can a therapy that requires a steady supply of donor eggs become practical?

Solomon and Egli believe so, as many existing research and assisted reproduction centers already rely on donor eggs.

A likely scenario for therapeutic use of SCNT derived patient specific cells would be similar to the existing approaches to bone marrow transplants or kidney donation. The patient would rely on a donor.